The present invention relates to a vehicle-body structure which comprises a front side frame extending in a vehicle longitudinal direction at a front part of a vehicle and having a closed cross section.
Conventionally, it is known that the front side frame is actively bent and impact energy is absorbed through bending deformation of this front side frame in a vehicle frontal collision (see Japanese Patent Laid-Open publication No. 2016-113084, for example).
The above-described patent document discloses a front side frame which includes a first region (where a bead is formed at an outward side wall portion, in a vehicle width direction, of the front side frame) which constitutes a compression-side wall portion and a tension-side wall portion through its outward-bending deformation when a load is inputted from a vehicle forward side and a second region (where a bead is formed at an inward side wall portion, in the vehicle width direction, of the front side frame) which constitutes a tension-side wall portion and a compression-side wall portion through its inward-bending deformation when the load is inputted from the vehicle forward side. Herein, there are provided a first reinforcing member which forms plural sub closed cross sections adjacent to each other in a vertical direction in cooperation with a main closed cross section of the above-described first region, a second reinforcing member which forms plural sub closed cross sections adjacent to each other in the vertical direction in cooperation with a main closed cross section of the above-described second region, and an engine mount member which is provided to partition across the above-described main closed cross section. Each of the above-described first and second reinforcing members comprises a first partitioning wall portion which partitions the above-described main closed cross section vertically and a second partitioning wall portion which is configured such that its vertical distance from the first partitioning wall portion on the tension side is smaller than its vertical distance from the first partitioning wall portion on the compression side. The above-described first and second reinforcing members are arranged adjacently, interposing a mount reinforcement therebetween. Thereby, a truss configuration is formed by contacting of respective compression-side end portions of the first and second tension-side partitioning portions which are supported at the tension-side wall portions of the first and second partitioning wall portions, so that sectional collapse which is caused by bending deformation is so suppressed that the absorbing efficiency of the impact energy can be increased.
However, in a case where a reinforcing member like the first and second reinforcing members of the above-described patent document is arranged inside the closed cross section of the front side frame, this reinforcing member is rectangular wavelike such that it protrudes alternately toward the tension-side wall portion and the compression-side wall portion and respective protrusion tip faces of its protrusion portions are joined to the tension-side wall portion and the compression-side wall portion by welding. Consequently, since many welding points are required at both of the tension-side wall portion and the compression-side wall portion, there is room for improvement in terms of the productivity of the front side frame.